The present invention relates to a dielectric waveguide filter and a mounting structure thereof. In particular, the present invention relates to a structure for mounting a dielectric waveguide filter having input and output electrodes to a printed circuit board formed with a conductive pattern to be brought into contact with the input and output electrodes.
Various dielectric waveguide filters can be obtained by variously coupling a plurality of dielectric waveguide resonators. In conventional dielectric waveguide filters, their input and output electrodes have been provided, for example, by forming conductive patterns in the sidewalls of dielectric resonators, or forming through holes in the dielectric resonators. However, such conventional structures of the input and output electrodes have suffered from mismatching in input and output sections due to poor continuity or connectivity at a connection area between the input and output electrodes and lines on a printed circuit board.
Considering this disadvantage, the applicant has proposed an improved structure of input and output electrodes in Japanese Patent Application No. 2000-329046 wherein a conductive strip (strip line) 85 made of a conductive film is provided in each of both end of dielectric block comprising a plurality of dielectric waveguide resonators as shown in FIGS. 8 and 9, and the conductive strip 85 are coupled with a conductive strip line 86 on a printed circuit board 86xe2x80x2.
However, this structure has need of extending each of the conductive strip up to the end surface of the dielectric block, and thereby the end face inevitably includes a region to which the dielectric substance of the dielectric block is exposed without forming a conductive film thereon. Such an exposed region of the dielectric substance causes leakage of electromagnetic field in the resonators, and the resulting radiation loss leads to significantly increased filer loss. In addition, desirable filter characteristics cannot be maintained without strict control of the positioning between the conductive strip and the conductive strip line.
It is therefore an object of the present invention to provide a dielectric waveguide filter capable of being desirably mounted on a printed circuit board with minimized discontinuity between input and output electrodes of the filter and a signal line on the printed circuit board so as to reduce undesirable losses otherwise caused by reflection or radiation of electromagnetic field at input and output sections.
It is another object of the present invention to provide a structure for mounting a dielectric waveguide filter to a printed circuit board, capable of achieving enhanced productivity with a simplified structure.
It is still another object of the present invention to provide a dielectric waveguide filter capable of maintaining its desirable characteristics even if some displacement occurs between a printed circuit board and the dielectric waveguide filter mounted on the printed circuit board.
In order to achieve the above object, the present invention is directed to provide an improved input and output structure for dielectric waveguide resonators, and further improve on the structure of a conductive pattern in a printed circuit board for mounting the dielectric waveguide resonators thereon.
Specifically, according to a first aspect of the present invention, there is provided a dielectric waveguide filter comprising a plurality of dielectric waveguide resonators in the form of rectangular parallelepiped-shaped blocks aligned as a single main body having opposite ends defined by respective the end blocks located thereat, and a pair of input and output electrodes provided in the end blocks, respectively, the main body having an outer surface including a bottom surface. In this dielectric waveguide filter, each of the end blocks is formed with a protruding portion including a dielectric substance extended from that therein, the protruding portion having an outer surface including a bottom surface and an end surface extending upward from the edge of the bottom surface. Each of the input and output electrodes is defined by a conductive strip line extending from the bottom surface of corresponding one of the end blocks to the edge region of the bottom surface of corresponding one of the protruding portions. These bottom surfaces have a region where the dielectric substance in contact with the both sides of the conductive strip line is exposed to outside. The end surface of the protruding portion has a region where the dielectric substance in contact with the conductive strip line is exposed to outside. Further, the outer surfaces of the main body and the protruding portions is covered with a conductive film excepting the regions where the dielectric substance in contact with the conductive strip line is exposed to outside.
According to a second aspect of the present invention, there is provided a structure for mounting a dielectric waveguide filter on a printed circuit board. In this mounting structure, based on the structure of the dielectric waveguide filter according to the first aspect of the present invention, the printed circuit board includes a pair of conductive patterns to be connected to the input and output electrodes, respectively, and the conductive patterns are formed on printed circuit board in alignment with one another. Further, the distance between the opposed ends of the conductive patterns is arranged to be less than the distance between the opposite outer edges of said input and output electrodes on the side of said end surfaces.
As above, the fundamental feature of a dielectric waveguide filter according to the present invention is as follows.
A. A plurality of dielectric waveguide resonators in the form of rectangular parallelepiped-shaped blocks aligned as a single main body having opposite ends defined by the end blocks located thereat.
B. A protruding portion provided to each of the end blocks serving as input and output terminals.
C. A conductive strip line extending from the bottom surface of corresponding one of the end blocks to the edge region of the bottom surface of corresponding one of said protruding portions.
In a specific embodiment of the present invention, conductive patterns each having the same width as that of each of the strip lines of the dielectric waveguide filter is formed on a printed circuit board, and each of the conductive patterns is arranged to terminate within the bottom surface of the main body. Thus, signals from the printed circuit board are coupled with a resonant mode in the dielectric waveguide filter by connecting the strip lines to the conductive lines. Each of the conductive patterns may be formed to extend between the opposing inner edges of the strip lines or input and output electrodes. In this case, even if the dielectric waveguide filter is mounted to the printed circuit board with some displacement in the longitudinal direction of the conductive pattern, the filter characteristics has no adverse effect.
In order to prevent the dielectric substance from being exposed to outside at a position closed to the dielectric waveguide resonators, each outer edge of the input and output electrodes of the dielectric waveguide filter can be shifted to a position away from dielectric waveguide resonators or the main body without forming the outer edges of the input and output electrodes in the end surfaces of the main body. Thus, the input and output electrodes or the conductive strip lines may extend up to the end surfaces of corresponding the protruding portions.
The dielectric waveguide filter according to the present invention can be mounted on a printed circuit board with enhanced continuity between input and output electrodes of the filter and a signal line on the printed circuit board, and thereby undesirable losses otherwise caused by reflection or radiation of electromagnetic field at input and output sections can be minimized. The mounting operation of the dielectric waveguide filter is also facilitated. In addition, the dielectric waveguide filter according to the present invention can be achieved only by modifying the configuration of the dielectric substance of the dielectric waveguide resonators. This advantageously provides lowered time and cost for designing.
Other features and advantages of the present invention will be apparent from the accompanying drawings and from the detailed description.